Colors bleed on textures

WSC

Is there a specifc for saving images to use for textures in Daz? For some reason, I always seem to have issues with some colors bleeding especially red.

cgidesign

Difficult to judge based on the small image. Maybe it is related to iray texture compression:

The compression in general works like explained below:

Medium Threshold: Any texture with a resolution below this or equal to this value will not get compressed
Inbetween Medium and High Threshold: Any Texture with a resolution in this range will get medium compression
High Threshold: Any texture with equal or greater resolution will get maximum compression

E.g. if you have a texture with resolution of 4096x4096 pixel and you set High Threshold to 4096 then you tell Iray to use max. compression. This can lead to visible compression artifacts.

If you don't want compression in this case you need to set Medium Threshold to more than 4096 (e.g. 4097) and High Threshold to e.g. 8192.

This way you tell Iray: any texture equal to or less than 4096 pixel will not get compressed, any texture inbetween 4096 and 8192 will get medium compressed, any texture equal or above 8192 gets maximum compressed.

A thread discussing the compession issue is here:

https://www.daz3d.com/forums/discussion/comment/7266671/#Comment_7266671

WSC

Ok, thanks. I'll take a look & test it out, but i'm not sure that's it. The color red seems to be the where it's an issue. I cropped it because the rest of it is not at issue.

PerttiA

Colour red often has problems with compression algorithms, the first time I stumbled on it was back in 97/98 with video editing

Spacious

That's definitely because of the Iray compression.  As stated above, you could fix it by doubling or quadrupling the Iray Compression thresholds, which has the drawback of drastically increasing vRAM usage for your render.

Alternately, if you're generally happy with the way surfaces look in your renders, and that particular surface is not taking up a lot of space in your current render frame, you could likely fix it by reducing the pixel size (in an external editor) of the image for that material.  Then it would be below the compression threshholds and would not get those artifacts.  This method will not help if the surface in question is taking up a lot of space in the render frame as it will then appear blocky and pixelated instead.

WSC

PerttiA said:

Colour red often has problems with compression algorithms, the first time I stumbled on it was back in 97/98 with video editing

Yes, red is generally the offender....

WSC

Spacious said:

That's definitely because of the Iray compression.  As stated above, you could fix it by doubling or quadrupling the Iray Compression thresholds, which has the drawback of drastically increasing vRAM usage for your render.

Alternately, if you're generally happy with the way surfaces look in your renders, and that particular surface is not taking up a lot of space in your current render frame, you could likely fix it by reducing the pixel size (in an external editor) of the image for that material.  Then it would be below the compression threshholds and would not get those artifacts.  This method will not help if the surface in question is taking up a lot of space in the render frame as it will then appear blocky and pixelated instead.

 

Thanks. I have not had a chance to try out "cgidesign's" reccomendation, but I'm indebted if it works.... Weird. I was under the assumption that more pixels would & image size would produce a better render....

WSC

cgidesign said:

Difficult to judge based on the small image. Maybe it is related to iray texture compression:

The compression in general works like explained below:

Medium Threshold: Any texture with a resolution below this or equal to this value will not get compressed
Inbetween Medium and High Threshold: Any Texture with a resolution in this range will get medium compression
High Threshold: Any texture with equal or greater resolution will get maximum compression

E.g. if you have a texture with resolution of 4096x4096 pixel and you set High Threshold to 4096 then you tell Iray to use max. compression. This can lead to visible compression artifacts.

If you don't want compression in this case you need to set Medium Threshold to more than 4096 (e.g. 4097) and High Threshold to e.g. 8192.

This way you tell Iray: any texture equal to or less than 4096 pixel will not get compressed, any texture inbetween 4096 and 8192 will get medium compressed, any texture equal or above 8192 gets maximum compressed.

A thread discussing the compession issue is here:

https://www.daz3d.com/forums/discussion/comment/7266671/#Comment_7266671

Thanks for your help! That was it. Weird that it only seemed to really affect red.

Spacious

In general, higher resolution texture images do make for better renders, but when the Iray compression kicks in it often has the opposite effect.  As you've discovered, you don't really notice the compressaion on some surfaces, and it's just horrible on others.

The trick to avoid compression artifacts is for the texture image size to be below the compression threshold.  You can raise the threshold or lower the texture image resolution.  Which solution works best depends on the situation.  It would be ideal if there was a way to adjust Iray compression on a surface by surface basis, but it doesn't work like that.